The present invention relates to tires and in particular to the bead regions of tires of the type disclosed in UK patent specification No. 1,584 553. Such tires incorporate an axially and radially inwardly projecting toe having two distinct physical properties which provide a unique bead retention feature even when fitted to a one piece wheel rim of the required type. Some tires of this type are known as "TD" tires.
The physical properties of the toe are: firstly a substantial form stiffness in the direction of the length of the toe so that the toe resists compressive force applied between the inward end of the bead toe and the bead reinforcement core and secondly a reasonable degree of flexibility perpendicular to its length when not under longitudinal compression to allow fitting and stripping of the tyre to and from its one piece wheel rim.
It has been discovered that one possible mode of dislodgement for tires of this type is for the bead to helix or spiral off its seat. In this action dislodgement or partial dislodgement past the groove towards the well at one part of the circumference advances circumferentially around the tire such that after a couple of reductions or more the bead has advanced inwards to the well and full dislodgement occurs. This may occur more readily if a part of the toe is not completely engaged in the groove or if an obstruction is in the groove.
One object of the present invention is to provide a means of avoiding problems of this type by modifying the toe of the tire to effectively decouple adjacent parts of the said toe in the circumferential direction.
According to the present invention a tire comprises a tread portion, sidewalls and a pair of spaced-apart beads each containing a substantially inextensible annular bead core, having bead seats and an extended toe portion comprising an elastomic material extending axially and radially inwards of the bead, the toe being rigid in the direction of its length so that in use of the tire on a wheel rim having a groove complementary to the toe and engaging the toe, when an axially outwardly directed force is generated at the bead core bead retention is affected. The toe of the tire is subdivided in the circumferential direction of the tire by a series of substantially radial cuts in the toe such that circumferentially adjacent portions of the toe are decoupled from one another and dislodgement or displacement of one of said portions does not displace an adjacent portion.
The radial cuts preferably each extend through the whole cross section of the toe. Alternatively the cuts may extend throughout less than 60% of the toe in which case the cuts preferably extend from the axially outer surface of the toe to the centre line of the length of the toe but not to the axially inner surface of the toe.
The cuts are preferably equally spaced around the circumference of the tire and there may be more than 6 cuts. The cuts may be very narrow and have substantially no width in the manner of tread sipes or may be wider but not more than 4 mm.